The Orichalcos God, or the Great Leviathan (4Kids dub), is a gigantic serpent creature who is behind all the events in Season 4 of Yu-Gi-Oh!, Waking the Dragons arc and thus is the one of the main antagonists the arc.
He was empowered by the dreaded Orichalcos magic and he employed the Orichalcos Stones to take over the world. It was these stones that made Dartz of Atlantis turn evil and use the Orichalcos Stones and cards to seek out victims to steal souls from to feed the Orichalcos God.
The souls of Gurimo, Pegasus J. Crawford, Yugi, Insector Haga, Dinosaur Ryuzaki, Amelda, Valon, Katsuya Jonouchi, Mai Kujaku, Rafael, and Seto Kaiba were among the many fed to the Orichalcos God. The final soul was that of Dartz himself, after he lost a duel to Yami.
Later, the remaining duelists' Duel monsters battled the Orichalcos God, but it was completely ineffective; the Orichalcos God sent numerous shards which easily dispatched all of them, while all the duelists were captured by him, except Yami. Yami, however, converted the darkness inside people and Duel Spirits' souls into light, allowing the three Egyptian gods to be released. It also greatly weakened the Orichalcos God, while the Egyptian gods' powers increased immensely. It required the souls and powers of millions to neutralize him; Yami finally caused him to disappear by removing all of his remaining darkness within his soul.
After the Orichalcos God's death, Dartz was released from his control, and the souls of all his victims were returned during the battle.
- He was also dubbed the "Grand Dragon Leviathan" in English advertisement media.
- On the Yugioh.com site, the artwork displayed for this monster is mistakenly that of "Cave Dragon".
- It is considering to be one of the largest monster that ever seen in the anime, being larger then all three Egyptian Gods.